I sometimes bleed after having sex. Is it normal?

If you are to dry, vaginally, that may cause lesions in your vaginal canal that will bleed nominally. If it is fresh blood, I wouldn't worry about it, unless you have something to worry about.

Not proper lubrication, too rough ? But no, you should not be bleeding

There are several reasons that might cause you to bleed, irritation from the sex being to rough and/or there not being enough lubrication as was mentioned. If you don't feel that either of those are an issue, check with your doctor. Sometimes infections can result in some bleeding after sex and of course would need to be treated.